1. Field of the Invention
The present invention relates to a method for inspecting the connection state of an electronic part and the substrate, and an apparatus for the same.
2. Description of the Prior Art
As known inspection methods according to the prior for the state of connection between an electronic part and a substrate, an electrical continuity inspection, a visual inspection and an X-ray inspection are existing.
The Japanese Published Patent No. 38501/1995 (published on Apr. 26, 1995 in Japan) discloses a technique whereby the part to be checked is irradiated with laser light and its connection state is judged according to its temperature rise. This technique will be described below as an example of the prior art.
FIG. 9 is a front cross-sectional view of a connection state inspecting apparatus for an electronic part and a substrate according to the conventional example.
The conventional apparatus shown in FIG. 9 consists of a laser light source 109, a lens 111, a detector 113 and a quality judgement unit 114.
A surface-mounted part 120, which is to be checked by this apparatus, consists of a package 126, pads 125 formed over the top surface of this package 126, and through holes 127 electrically connected to these pads 125 and penetrating the package 126 downward. Each of the through holes 127 is connected to the upper surface of a substrate 107 by solder connecting portions 104.
In this apparatus according to the prior art, the pads 125 are irradiated with a laser beam 110, radiated infrared rays 112 from the pads 125 are received to measure the increment of a temperature character value Va. This increment is compared with a preset increment to evaluate the connection state of the solder connecting portions 104.
This conventional apparatus is characterized in that the pads 125 and the through holes 127 are structurally added afterward to the package 126 to heat the solder connecting portions 104 which are not exposed on the surface and accordingly cannot be irradiated with the laser beam 110. The solder connecting portions 104 are thermally coupled to the pads 125 by the through holes 127.
However, this conventional apparatus has the following problems.
First, the need to form the pads 125 and the through holes 127 within the package 126 for the sole purpose of inspecting the connection state significantly limits the arrangement of wiring routes in the package 126.
Second, a step to bore many through holes 127 into the package 126, a step to fill these through holes 127 with electroconductive material and a step to form a pad 125 over the top of each through hole 127 are indispensable merely for inspecting the connection state. This results in a substantial increase in the number of required steps in the manufacturing process and a corresponding increase in production cost.
Third, the low intensity of the radiated infrared rays 112 emitted by the temperature rise of the pads 125 brings down the accuracy of quality of judgement.
Thus, a plating layer of metal, such as nickel or gold, is usually formed over the surface of each of the pads 125. These metals have the extremely low infrared emission character of any such metal invites a very low intensity of the radiated infrared rays 112 emitted from the pads 125 themselves even if the temperature of the pads 125 rises.
Fourth, a high intensity of unnecessary infrared rays scattered over the surfaces of the pads 125 brings down the accuracy of quality judgement.
Because gold has very high infrared reflection character, the reflected light on the pads 125 is incident into the detector 113 as noise components.
In view of these problems, a first object of the present invention is to provide a method for inspecting the connection state of an electronic part and a substrate and an apparatus for the same which permits judgement of the quality of the connection state at high accuracy without needing structural addition of through holes and pads for use in connection state inspection.
A second object of the present invention is to provide a method for inspecting the connection state of an electronic part and a substrate and an apparatus for the same which permits judgement of the quality of the connection state at high accuracy even where the terminals for electrical inspection of the part to be inspected are gold-plated or otherwise and accordingly poor in infrared emission character.
A method for inspecting a connection state of an electronic part and a substrate, the electronic part having a terminal for electrical inspection electrically connected to a solder connecting portion, and being connected to a surface of the substrate by the solder connecting portion, has the steps of: heating a first specific position on the electronic part, measuring a temperature rise of a second specific position thermally coupled to the first specific position, and judging the quality of the connection state of the solder connecting portion by comparing the measured temperature rise and a reference temperature rise.
An apparatus for inspecting a connection state of an electronic part and a substrate, the electronic part having a terminal for electrical inspection electrically connected to solder connecting portion, and being connected to a surface of the substrate by the solder connecting portion, has: a heating unit for heating a first specific position on the electronic part, a thermometer for measuring a temperature rise of a second specific position thermally coupled to the first specific position, and a quality judgement unit for judging the connection state of the solder connecting portion by comparing the measured temperature rise with a reference temperature rise.
By the adoption of such the method and the apparatus, the invention makes possible to judge the connection state by using the terminals for electrical inspection, which are previously formed thereon.
Even where the infrared emission character of the terminals is low, the quality of the connection state can be judged on the basis of the temperature rise on specific positions thermally connected to these terminals.